When sawing concrete, brick, stone, wood, plasterboards and similar materials, dust is generated, usually large amounts thereof. Many devices of different type are employed in order to prevent, as far as that is possible, but the dust is scattered to the environment, while other devices have been suggested but have not been used. Thus devices exist, whos mode of working, according to a known principle, makes use of a hood-shaped blade guard or the like, which surrounds the saw blade and in which dust is collected and is sucked away to a vacuum device via a hose, which is connected to the blade guard. A machine and a device of that kind is disclosed in WO 02/100597. It is typical and necessary that this known hood-shaped blade guard completely surrounds that part of the saw blade which is not located in the work piece, and that the blade guard contacts the surface of the work piece, which surface is supposed to be essentially flat, and with good sealing action, in order that the device shall function well as a dust collector. The blade guard thus shall function like a suction box, in which a sufficient underpressure must be maintained in order to suck up into the blade guard that dust which is generated in the kerf and which is not thrown backwards-upwards by the tool. At the same time, dust must not be scattered to the environment from the kerf and/or due to leakage between the blade guard and the top surface of the work piece. In connection with devices which are based on this principle, however, some fundamental problems are encountered. The first problem is that the volume in the suction box, i.e. the interior volume of the hood-shaped blade guard, is comparatively large, which is a drawback because it makes it more difficult to maintain a necessary underpressure in the suction box, which in turn jeopardises its suction capacity. The second problem is that the device will not function at all during an initial phase of a working operation, when a kerf has not yet been established in a work piece to a sufficient depth. During this phase, the blade guard can not seal satisfactorily against the work piece, which means that most of the dust will be scattered to the environment. This is particularly true when working in concrete, brick, stone, plasterboards and the like by means of cutter disks which generate a large amount of very fine dust. Therefore, it can be impossible to work in such materials in furnished or from other reasons sensitive premises with this type of devices, if the dust collector is not supplied with auxiliary means for preventing scattering of dust. Therefore it is common practise to successively spray water into the kerf as the kerf is being formed, in order to bind the dust, preventing it to be scattered to the environment, such as according to said WO 02/100597. This however, causes a slurry to be generated, which gives rise to a new problem.
U.S. Pat. No. 5,167,215 discloses a wheel carried concrete sawing saw, which also includes an apparatus for collecting and evacuating the dust which is generated when sawing in concrete. This apparatus is equipped with an auxiliary unit allowing collection of dust also during the initial phase of a sawing operation. The auxiliary unit consists of a funnel, which is pivotally connected to a blade guard and provided with a lower, transversal edge, which contacts the top surface of the work piece, sliding against said top surface behind the saw blade when the machine is moving forwards and the saw blade is working in the work piece. Said “funnel” is turned upwards-rearwards behind the blade guard, when the blade proceeds deeper and deeper into the work piece. The intention with the apparatus is that the concrete dust which is produced during the sawing operation shall be thrown rearwards-upwards into said “funnel” and then be sucked away from the funnel through a suction hose connected to the apparatus. The method is based on the premise that the saw blade will act as an efficient sling and that the trailing device will collect essentially all the concrete dust that is generated during the sawing operation. This assumption, however, appears to be based on an underestimation of the capacity of concrete dust to scatter from spaces, e.g. the kerf itself, which are not subject to an effective underpressure relative to the surrounding space. The apparatus and the machine according to U.S. Pat. No. 5,167,215 therefore do not provide an acceptable solution of the dusting problem in connection with sawing concrete and similar materials. Besides, it is not possible to work more than in one direction—forwards—by means of this machine and apparatus, which is another inconvenience.